Gila monster venom contains a peptide that stimulates pancreatic enzyme secretion probably by a mechanism involving interaction with vasoactive intestinal peptide receptors on pancreatic acinar cells. Four peptides have been isolated from venom sacs of two species of yellow jackets and their amino acid composition determined. Three of the peptides lyse liposomes indicating that they will cause mast cell degranulation. The European hornet contains a peptide which depolarizes human neutrophil membranes without causing cell death. The peptide also causes the cells to secrete their granular contents suggesting a pro-inflammatory activity. Of no less interest, the peptide blocks chemoattractant-induced secretion of the cells. Metenkephalin blocks the action of ranatensin on the guinea pig ileum probably at the level of the ranatensin receptor. Numerous columns and mobile phases have been evaluated for the HPLC analysis of peptides. Best results (resolution, recovery, sensitivity) were obtained with Toyo Soda TSK LS-41 columns and a mobile phase consisting of trifluoracetic acid, triethylamine, water, and acetonitrile. With many peptides as little as 0.2 Mug could be detected.